An aircraft in flight generates two wake vortices in its wake. Starting from the wings, the vortices tend first of all to move closer to one another, and then to maintain a more or less constant distance from one another while at the same time losing altitude with respect to the altitude at which they were generated.
The formation of wake vortices behind an aircraft is well known and documented, and the position of the centers of the vortices generated by an aircraft is acquired in particular by calculating their descent speed. This depends on flight parameters of the aircraft, such as mass, altitude, roll angle, aerodynamic configuration, size, air density at the flight point, speed, etc.
It is beneficial for an aircraft, termed intruder aircraft, to be able to precisely calculate the positions of the vortices generated in the wake by an aircraft, termed lead aircraft, in order:                to fly in formation behind the lead aircraft while drawing maximum benefit from the updraughts in the vortices in order to reduce its fuel consumption; or        to avoid being subjected to turbulence caused by the vortices.        
For an intruder aircraft flying in formation behind a lead aircraft, it is additionally beneficial to calculate the flow strength of the wake vortices generated by the lead aircraft, so as to position itself effectively in the updraughts of the vortices. The flow strength is also able to be calculated through knowledge of the flight parameters of the lead aircraft, such as mass, size, air density at the flight point, speed, etc.
In a known manner, aircraft that are close to one another communicate data between one another in an automated manner, in particular via an active collision avoidance device of TCAS (Traffic Collision Avoidance System) type. Such a system fitted on an aircraft is able to monitor up to forty-five other aircraft flying within a monitoring volume of the TCAS and, as a result, the bandwidth of the automated data communications between the aircraft has to be restricted such that only the altitude, necessary for predicting a risk of collision, is exchanged. As a result, on account of the bandwidth restriction, the flight parameters necessary for calculating the descent speed of the centers of the vortices generated by the lead aircraft or for calculating the flow strength of the wake vortices are not able to be transmitted to the intruder aircraft.